Entering Roughness Coefficients

The roughness of a culvert will have a significant
effect on the flow through the culvert. The energy loss due to the hydraulic
resistance or roughness of a culvert is part of the "hydraulic price"
of flow through a pipe. Two commonly used equations to describe the flow
as a function roughness in a culvert are the Darcy
equation and the Manning
equation. In these equations the roughness is represented with a resistance
or roughness
coefficient, either Manning's n or the Darcy Friction Factor.

Manning's n

FishXing uses Manning's n as a default resistance
coefficient for both culvert material and bottom material, when different.
FishXing will require you to enter a Bottom Roughness if the culvert installation
is Embedded or if the selected culvert shape is an open bottom structure
(High /Low Profile Arch, Single Radius Arch or Metal Box). FishXing then
computes a Composite
Roughness for determining flow resistance in the hydraulic calculations.

To select a roughness coefficient for the Culvert
and for the Bottom Material use the drop down menu or by entering your
own estimate. FishXing provides default values of roughness only when
using Manning's n.

An expanded table of Manning's
n values is available by pressing the Ellipsis Button to the right
of the field. These are provided as a reference and are not directly selectable.
You must type in the desired value or copy and paste from the table using
the Ctrl+C and Ctrl+V commands respectively.

Darcy and Chezy Friction Factor

You can change the resistance method used by for
hydraulic calculations by selecting Roughness
Calculations in the Options
menu on the Navigation
Bar. If the Darcy-Weisbach
Friction Factor or the Chezy Coefficient is selected you may only
enter a single roughness coefficient for the culvert, even if it is embedded.
When values are available the Darcy or Chezy methods can be used to model
Baffle Hydraulics in the culvert.